Time temperature indicators (alternatively called “time temperature integrators”) are devices that are characterized by at least one changeable observable physical property that progresses at a rate that is proportional to the temperature or at a rate that is proportional to the temperature and the time, and thus provide an indication of the full or partial time-temperature history of their immediate surroundings. Time temperature indicators (TTIs) are simple and inexpensive devices, typically designed as labels. When attached to a perishable good, a TTI (appropriately designed and calibrated) monitors its time-temperature history and provides a simple, usually visual, straightforward summary of the exposure history of the product to time-temperature, thereby providing indication of the product's freshness condition. Consequently, TTIs are among the most promising shelf-life-report technologies.
The TTI concept was developed to ensure the safety and quality of perishable goods, such as food and drug products, throughout their entire lifespan, from manufacturing to the time they are consumed by the end-user. The safety and quality of many perishable goods such as food, drugs, vaccines and blood, depend mainly on appropriate storage conditions during distribution and storage. Different factors such as gas composition, relative humidity and temperature affect their real lifetime. The fact that changing conditions affect the effective shelf-life of these kinds of goods is not reflected by a “best before . . . ” type label that relies on appropriate storage conditions. Of all storage factors, temperature abuse is the most frequently observed factor for deterioration, based on diverse physical, chemical, enzymatic or microbial processes. Therefore, the TTI technology can provide a simple tool for controlling the food and drug supply-chain. The color and/or other visual physical properties of the TTI varies as a function of the time at a rate which is temperature dependent or time-temperature dependent, thus providing an active scale of “freshness” of the product to which it is attached, by comparing the color (or darkness) or any other varying visual property of the TTI label with a given comparative scale. Since the TTI indicators may be designed to provide a distinct “Yes” or “No” type of answer regarding the time temperature factor, they may provide an important “clear cut” answer and save further elaborate data inspection. This is ideal for HACCP (Hazard Analysis Critical Control Point), where the emphasis is on real time decision making and action.
Various TTIs are disclosed, for example in the following patent publications. U.S. Pat. No. 4,737,463 discloses a photoactivatable time-temperature indicator based on diacetylenic salts. A thermally unreactive (“inactive”) diacetylenic salt (or a mixture of such salts) is mixed, in a polymeric matrix, with a material that generates acid upon exposure to light. Photoexcitation, preferably by UV or near UV light, causes the formation of a thermal reactive (“active”) free diacetylenic acid. Following this activation step, a progressive color development occurs at a rate that increases with temperature. The indicator is useful for monitoring the freshness of perishable products, particularly those that require refrigeration.
WO 99/39197 discloses a technique, which provides a substrate for packaging time- and temperature-sensitive products or for application thereon. According to this technique, planar time-temperature integrator is used consisting of a matrix and at least one reversible indicator embedded therein being arranged in the area of the substrate. The indicator has photochromic properties.
U.S. Pat. No. 6,435,128 discloses a time-temperature integrating indicator device that provides a visually observable indication of the cumulative thermal exposure of an object. The device includes a substrate having a diffusely light-reflective porous matrix and a backing. The backing includes on its surface a viscoelastic indicator material for contacting the substrate and a barrier material for substantially inhibiting the lateral and longitudinal flow of viscoelastic indicator material between the substrate and the backing.
U.S. Pat. No. 6,042,264 discloses a time-temperature indicator device, designed as a label, for measuring the length of time to which a product has been exposed to a temperature above a pre-determined temperature. The period of time of exposure is integrated with the temperature to which the indicator is exposed. The label is a composite of a plurality of layers adapted to be adhered at its underside to a product container. The label includes a printable surface layer, a longitudinal wicking strip that is adhered underneath the surface layer substantially at the opposite extremities only of the wicking strip and a lower substrate layer forming an envelope with the surface layer. A heat-fusible substance, which melts and flows above a pre-determined temperature, is applied on the surface of the wicking strip contiguous to at least one of the ends of the wicking member. When the heat-fusible substance is exposed to a temperature above the pre-determined temperature, the heat-fusible substance flows along the length of the wicking member. The label has a printable surface layer and is sealed at its peripheral edge to the peripheral edge of the substrate layer. These layers encapsulate the wicking member and the heat-fusible substance. The surface layer is provided with a sight window at an intermediate location over the wicking member through which the progress of flow on the wicking member is observed.
PCT Publication Application No. WO 03/077227 discloses a time indicating label comprising a label substrate having first and second surfaces, an acid-based indicator composition, and an activator composition. One of the acid-based indicator composition and the activator composition is on the first surface of the substrate, and both of these compositions when brought in contact remain adhered. The label may have a pressure sensitive adhesive on the second surface of the label. The label provides an effective means for determining the safety of frozen foods. The labels also provide a means of providing security by providing name badges that are time sensitive and may not be reused. The name badges provide a means to monitor the length of a visitor's time and prevent reusing the name badge.
PCT Publication Application No. WO 03/044521 discloses a sensor adapted to be remotely readable by RF techniques for identification of the quality of a packaged foodstuff. The sensor either reacts with compounds generated in the atmosphere of the foodstuff package due to the microbiological decay of the foodstuff, for example hydrogen sulfide or other sulfide compounds, or the sensor is responsive to an increased oxygen content in the atmosphere of the package due to a leakage in the package. The sensor is based on a RF circuit. Oxygen or the microbiologically generated gas affects the electrical properties of the circuit material. For example, the resistor, the capacitor or the inductive coil of the circuit or at least a fraction thereof are made of silver, iron, aluminum, a redox-type indicator-dye, a conductive polymer, or copper. Due to the reaction of the aforementioned gases with these materials, the sensor resistance, conductivity, capacitance and/or inductance of the respective sensor elements changes depending on the amount of the disintegrating gas.
PCT Publication Application No. WO 01/25472 discloses a biosensor useful to monitor the time and temperature to which a product has been exposed. The biosensor is based on a RF circuit comprising a unit, which changes its conductivity/resistance as a function of time and temperature. This unit comprises an enzyme and a substrate, wherein the enzyme is adapted to affect the substrate so that its conductivity increases as a function of time and temperature. Thus, a biosensor is disclosed, whose RF circuit can be activated by applying, for instance, a magnetic field over the same to generate a measurable current, which is dependent on the total resistance of the circuit and which thus varies as a function of the time and temperature to which the unit of the biosensor has been exposed.
PCT Publication Application No. WO 95/33991 discloses a condition indicator for perishable goods. The indicator comprises sensor means for gas or vapor associated with decay or contamination affecting an electrical property of the sensor means, which are incorporated into an electrical circuit measuring the property. The electrical circuit disclosed in WO 95/33991 is not a RF circuit. That means the sensor changes are not remotely readable. The circuit may be printed. The sensor may comprise a semiconducting material such as polypyrroles, which change an electrical property such as resistance or impedance on exposure to certain gases.